Steel shelving units comprising horizontal shelf-supporting beams with ends adjustably connected to vertical support columns for shelf height adjustment are known. While such units are very useful, it is desirable to provide such beams with improved structures for converting such beams to such columns. As well, it is frequently desirable to provide additional capacity in such units for holding items other than by positioning on the shelves themselves. Additionally, it is desired to provide for vertical adjustability of shelf unit accessories providing such additional capacity.